The present invention relates to signalling in a telecommunications network and more particularly to the provision of a call control protocol which is independent of the signalling traffic bearer.
Current telecommunications networks currently rely to a large extent upon the Signalling System no.7 (SS7) as the mechanism for controlling call connections and for handling the transfer of signalling information between signalling points of the networks. Typically, one or more application and user parts at a given signalling point will make use of SS7 to communicate with peer application and user parts at some other signalling point. Examples of user parts are ISUP (ISDN User Part) and TUP (Telephony User Part) whilst examples of application parts are INAP (Intelligent Network Application Part) and MAP (Mobile Application Part). The conventional SS7 protocol stack includes Message Transfer Parts MTP 1, MTP 2, and MTP 3 which handle the formatting of signalling messages for transport over the physical layer as well as various routing functions.
There has been considerable interest of late amongst the telecommunications community in using non-standard (i.e. non-conventional within the telecommunications industry) signalling transport mechanisms in telecommunications networks in place of the conventional SS7 mechanisms. The reasons for this are related both to improvements in efficiency as well as potential cost savings. Much consideration has been given for example to the use of Internet Protocol (IP) networks to transport signalling information between signalling points. IP networks have the advantage that they make efficient use of transmission resources by using packet switching and are relatively low in cost due to the widespread use of the technology (as opposed to specialised telecommunication technology). There is also interest in using other transport mechanisms including AAL1/2/5, FR etc.
The standard ISUP which deals with the setting-up and control of call connections in a telecommunications network is closely linked to the SS7 signalling transport mechanism and does not readily lend itself to use with other non-standard transport mechanisms such as IP and AAL2. As such, several standardisation bodies including the ITU-T, ETSI, and ANSI, are currently considering the specification of a signalling protocol for the control of calls, which is independent of the underlying transport mechanism. This can be viewed as separating out from the protocol bearer control functions which relate merely to establishing the parameters (including the start and end points) of the xe2x80x9cpipexe2x80x9d via which user plane data is transported between nodes, and which are specific to the transport mechanism. The new protocol, referred to as Transport Independent Call Control (TICC), retains call control functions such as the services invoked for a call between given calling and called parties (e.g. call forwarding), and the overall routing of user plane data.
The inventors of the present invention have recognised that different signalling transport mechanisms such as IP, AAL2 , AAL5 and the like will have different requirements for the interface with the higher TICC protocol. For example, different transport mechanisms may expect to send and receive different sized data packet units to and from the higher protocol layers. In order to make TICC fully independent of the signalling transport mechanism therefore, it is necessary to introduce an adaptation layer between the TICC and the signalling transport mechanism.
According to a first aspect of the present invention there is provided a signalling point of a telecommunications network, the signalling point comprising:
a Transport Independent Call Control (TICC) part;
a signalling transport part arranged to couple call control signalling information between said TICC and peer TICC part at a remote signalling point; and
a signalling transport converter arranged logically between said TICC part and said signalling transport part and arranged to present a standard interface to the TICC part and a specific interface to the signalling transport part, wherein said call control signalling is exchanged between the TICC part and the signalling transport part via the signalling transport converter.
Embodiments of the present invention enable the TICC to be standardised in a form which enables the TICC to be used with any signalling transport part. Generic message primitives are exchanged between the TICC and the signalling transport converter whilst specific message primitives are exchanged between the signalling transport converter and the signalling transport part. The signalling transport converter (STC) depends to some extent upon the signalling transport part (STP). The TICC assumes certain functionality of the STC/STP combination but does not necessarily care whether the functionality is provided by the STC or the STP. In certain embodiments, the signalling transport converter may deal with any adjustments in Packet Data Unit (PDU) size, e.g. the segmentation of TICC messages, and with any address transformations.
Preferably, the signalling point comprises a Bearer Control (BC) part which is separate from the TICC part, the BC part being arranged to exchange information with a peer BC part. The BC part is arranged inter alia to define and establish a pipe on a link between two nodes of the network and through which user plane data is transported.
According to a second aspect of the present invention there is provided a method of transporting signalling information between peer Transport Independent Call Control (TICC) parts located at respective signalling points of a telecommunications network, the method comprising transferring signalling information between a TICC part and a signalling transport part at the same signalling point by exchanging the signalling information between the TICC part and a signalling transport converter in the form of generic message primitives, and exchanging the signalling information between the signalling transport converter and the signalling transport part in the form of specific message primitives.